1. Field of the Invention
This invention relates to mobile communications and, more particularly, to the use of a proxy switch in a mobile communication network to improve capacity and cost-effectiveness of the communications network and to offer a platform for new mobile services.
2. Discussion of Related Art
All modern mobile communication systems have a hierarchical arrangement, in which a geographical xe2x80x9ccoverage areaxe2x80x9d is partitioned into a number of smaller geographical areas called xe2x80x9ccells.xe2x80x9d Referring to FIG. 1, each cell is preferably served by a Base Transceiver Station (BTS) 102a. Several BTS 102b-n are aggregated via fixed links 104a-n into a Base Station Controller (BSC) 106a. The BTSs and BSC are sometimes collectively referred to as the Base Station Subsystem (BS) 107. Several BSCs 106b-n may be aggregated into a Mobile Switching Center (MSC) 110 via fixed links 108a-n. 
The MSC 110 acts as a local switching exchange (with additional features to handle mobility management requirement, discussed below) and communicates with the phone network (PSTN) 120 through trunk groups. Under U.S. mobile networks, there is a concept of a home MSC and a Gateway MSC. The home MSC is the MSC corresponding to the exchange associated with a Mobile Station (MS); this association is based on the phone number, e.g., area code, of the MS. (The home MSC is responsible for the HLR discussed below). The Gateway MSC, on the other hand, is the exchange used to connect the MS call to the PSTN. Consequently, some times the home MSC and the Gateway MSC are the same entity, but other times they are not (e.g., when the MS is roaming). Typically, a Visiting Location Register (VLR) 116 is co-located with the MSC 110 and a logically singular HLR is used in the mobile network. As will be explained below, the HLR and VLR are used for storing many types of subscriber information and profiles.
Briefly, a number of radio channels 112 are associated with the entire coverage area. The radio channels are partitioned into groups of channels allocated to individual cells. The channels are used to carry signaling information to establish call connections and the like, and to carry voice or data information once a call connection is established.
At a relatively high level of abstraction, mobile network signaling involves at least two main aspects. One aspect involves the signaling between an MS and the rest of the network. With 2G (xe2x80x9c2Gxe2x80x9d is the industry term used for xe2x80x9csecond generationxe2x80x9d) and later technology, this signaling concerns access methods used by the MS (e.g., time-division multiple access, or TDMA; code-division multiple access, or CDMA), assignment of radio channels, authentication, etc. A second aspect involves the signaling among the various entities in the mobile network, such as the signaling among MSCs, VLRs, HLRs, etc. This second part is sometimes referred to as the Mobile Application Part (MAP) especially when used in the context of Signaling System No. 7 (SS7).
The various forms of signaling (as well as the data and voice communication) are transmitted and received in accordance with various standards. For example, the Electronics Industries Association (EIA) and Telecommunications Industry Association (TIA) help define many U.S. standards, such as IS-41, which is a MAP standard. Analogously, the CCITT and ITU help define international standards, such as GSM-MAP, which is an international MAP standard. Information about these standards is well known and may be found from the relevant organizing bodies as well as in the literature, see, e.g., Bosse, Signaling in Telecommunications Networks (Wiley 1998).
To deliver a call from an MS 114, a user dials the number and presses xe2x80x9csendxe2x80x9d on a cell phone or other MS. The MS 114 sends the dialed number indicating the service requested to the MSC 110 via the BS 107. The MSC 110 checks with an associated VLR 116 (more below) to determine if the MS 114 is allowed the requested service. The Gateway MSC routes the call to the local exchange of the dialed user on the PSTN 120. The local exchange alerts the called user terminal, and an answer back signal is routed back to the MS 114 through the serving MSC 110 which then completes the speech path to the MS. Once the setup is completed the call may proceed.
To deliver a call to a MS 114, (assuming that the call originates from the PSTN 120) the PSTN user dials the MS""s associated phone number. At least according to U.S. standards, the PSTN 120 routes the call to the MS""s home MSC (which may or may not be the one serving the MS). The MSC then interrogates the HLR 118 to determine which MSC is currently serving the MS. This also acts to inform the serving MSC that a call is forthcoming. The home MSC then routes the call to the serving MSC. The serving MSC pages the MS via the appropriate BS. The MS responds and the appropriate signaling links are setup.
During a call, the BS 107 and MS 114 may cooperate to change channels or BTSs 102, if needed, for example, because of signal conditions. These changes are known as xe2x80x9chandoffs,xe2x80x9d and they involve their own types of known messages and signaling.
One aspect of MAP involves xe2x80x9cmobility management.xe2x80x9d Briefly, different BSs and MSCs may be needed and used to serve an MS, as the MS 114 roams to different locations. Mobility management ensures that the Gateway MSC has the subscriber profile and other information the MSC needs to service (and bill) calls correctly. To this end, MSCs use a Visiting Location Register (VLR) 116 and a Home Location Register (HLR) 118. The HLR is used to store and retrieve the mobile identification number (MIN), the electronic serial number (ESN), MS status, and the MS service profile, among other things. The VLR stores similar information in addition to storing an MSC identification that identifies the Gateway MSC. In addition, under appropriate MAP protocols, location update procedures (or registration notifications) are performed so that the home MSC of a mobile subscriber knows the location of its users. These procedures are used when a MS roams from one location to another or when a MS is powered on and registers itself to access the network. For example a location update procedure may proceed with the MS 114 sending a location update request to the VLR 116 via the BS 107 and MSC 110. The VLR 116 sends a location update message to the HLR 118 serving the MS 114, and the subscriber profile is downloaded from the HLR 118 to the VLR 116. The MS 114 is sent an acknowledgement of a successful location update. The HLR 118 requests the VLR (if any) that previously held profile data to delete the data related to the relocated MS 114.
FIG. 2 shows in more detail the signaling and user traffic interfaces between a BS 107 and an MSC 110 in a CDMA mobile network. The BS 107 communicates signaling information using the A1 interface. The A2 interface carries the user traffic (e.g., voice signals) between the switch component 204 of the MSC and the BS 107. The A5 interface is used to provide a path for user traffic for circuit-switched data calls (as opposed to voice calls) between the source BS and the MSC.
As the number of cell sites or the number of subscribers grows, the load on the MSC 110 increases. This increased load forces the service provider to add more capacity to the system. Typically, to add more capacity, the service provider adds more switch modules to the MSC or deploys additional MSCs in the network. Either alternative involves significant cost.
Moreover, subscribers are demanding newer services, e.g., xe2x80x9cdata callsxe2x80x9d to the Internet. For some of these services MSCs are not cost effective because they were primarily designed for voice calls. Integration of new services into the MSC is complicated or infeasible because of the proprietary and closed designs used by many MSC software architectures. That is, the software logic necessary to provide the services is not easy to add to the MSC 110. Often, a switch adjunct is used to provide such services. For example, an Inter-Working Function (IWF) is an adjunct to route a data call to the Internet. Either approachxe2x80x94integrating functionality into the MSC or adding a trunk-side adjunctxe2x80x94involves the MSC in the delivery of service. Since the new service is expected to spur demand, integrating new services via MSC design changes or through trunk-side adjuncts is likely to exacerbate network congestion at the MSC and require costly MSC resources.
The invention provides systems and methods of mobile communication. In particular, switching operations are performed between at least one mobile switching center (MSC) and at least one base station subsystem (BS). The switching, according to one aspect of the invention, allows communication traffic to be siphoned to or from an alternative network. Consequently, the number of messages sent from the BS may not correspond to the number of messages received by an MSC, e.g., because they are siphoned to an alternative network. Thus, according to one aspect of the invention, the switching provides fault management within such an environment by providing FSN and BSN counters at a proxy switch between a BS and MSC.
According to one aspect of the invention, fault management is provided for a mobile communications network having at least one BS, at least one MS, at least one MSC, and at least one switch in communication with at least one of the base station subsystems and at least one of the MSCs. The switch provides a forward sequence number counter (FSN) and a backward sequence number counter (BSN) for communication with the MSC, and a FSN and BSN for communication with the BS. As messages are received and sent by the switch, the switch maintains the corresponding pair of FSN and BSN in accordance with the messages. The switch detects whether a received message is a change over order message (COO) from one of the MSC and BS, indicating a break in a first signaling link between the switch and the one of the MSC and BS, and forces a break in a second signaling link between the switch and the other of the MSC and BS, which corresponds to the first signaling link. The switch generates and sends a new COO message to the other of the MSC and BS. The switch receives a change over acknowledge (COA) message from the other of the MSC and BS, and the switch generates and sends a new COA message to the one of the MSC and BS in which the new COA message contains the BSN maintained by the switch for communication with the one of the MSC and BS.
Under another aspect of the invention, a proxy switch includes signaling message handling logic for receiving signaling messages from the MSC and BS in accordance with said mobile signaling protocol. Message transmission logic issues messages to the MSC and BS. A FSN and a BSN are provided for communication with the MSC, and another FSN/BSN pair are provided for communication with the BS. Logic detects whether a received message is a change over order message (COO) from one of the MSC and BS, indicating a break in a first signaling link between the proxy switch and the one of the MSC and BS, and logic generates and sends a COA message to the one of the MSC and BS containing the BSN maintained by the switch for communication with the one of the MSC and BS. Fault emulation logic forces a break in a second signaling link between the proxy switch and the other of the MSC and BS, wherein the second signaling link is configured to correspond to the first signaling link, and generates and sends a new COO message to the other of the MSC and BS.